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From: Tim Schmielau <>
To: Johann Schuster <>
Subject: Re: Measuring cpu time using getrusage
Date: Sat, 17 Feb 2007 13:09:58 +0100 (CET)	[thread overview]
Message-ID: <> (raw)
In-Reply-To: <>

On Wed, 14 Feb 2007, Johann Schuster wrote:

> currently i'm trying to measure the cpu times for
> numerical algorithms written in C using two calls of
> getrusage() and then calculating the time difference.
> According to the man page of getrusage i looked at the
> user time of my process. Surprisingly the measured user
> times vary strongly depending on the system load of the
> machine.
> A heavy system load nearly doubles the measured time
> for my routine.

Does your system have hyperthreading? (look at whether the siblings field 
in /proc/cpuinfo is greater than one)
If yes, there is no way to accurately measure runtimes because the 
(single-threaded) performance of your CPU depends on the other tasks 
running. Just disable hyperthreading for these measurements.


      reply	other threads:[~2007-02-17 12:10 UTC|newest]

Thread overview: 2+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2007-02-14 13:17 Johann Schuster
2007-02-17 12:09 ` Tim Schmielau [this message]

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